A forensic pathologist who performed a second autopsy on Drew Peterson's third wife years after she was found dead in her dry bathtub testified Thursday that there's just one plausible explanation for her death: She was murdered.

But under aggressive questioning by the defense, Dr. Larry Blum conceded that some of his well-respected counterparts disagreed and still maintained her death was an accident.

A coroner initially ruled Kathleen Savio died in an accidental fall in her bathtub. Her 2004 death was reclassified a homicide only after Peterson's fourth wife, Stacy Peterson, vanished in 2007 and Blum did his new examination.

Testifying for a second day Thursday, Blum told jurors he didn't believe an accidental fall could explain how Savio had a fresh gash on the back of her head and a pattern of deep bruises on the front of her body.

"I couldn't see how that could happen," Blum testified.

Blum, a key witness for the state, was subject to aggressive questioning by the defense later in the day. Over the objections of prosecutors, the judge let defense attorney Ralph Meczyk ask if three other pathologists who reviewed autopsy data still held Savio died accidentally.

"Despite their opinion, you say homicide?" the attorney asked.

"I haven't changed my opinion," Blum responded.

Blum also denied Meczyk's suggestion that he manipulated his autopsy results to mesh with Will County State's Attorney James Glasgow's theory that Savio was murdered.

Blum testified earlier that Savio's circular tub also had no edges pronounced enough to cause the two-inch, straight-line wound on her head. Also, the position of Savio's body in the tub -- face down and with her feet jammed against the sides of the tub -- did not support a theory that she slipped and hit the back of her head, he said.

Peterson, a 58-year-old former suburban Chicago police officer, has pleaded not guilty to first-degree murder in Savio's death. He is also a suspect in Stacy Peterson's disappearance, although he has never been charged in her case. Authorities presume she is dead, though a body has never been found.

Peterson's attorneys maintain the original, 2004 autopsy on Savio's body by Dr. Bryan Mitchell was sound and that his finding of an accidental death holds up. Mitchell died in 2010.

Under cross examination Meczyk, Blum conceded that the coroner who deemed Savio's death accidental had been respected in the field.

"He did an orthodox and professional autopsy?" the attorney asked.

"Yes, sir," Blum responded.

Earlier in the day, Blum testified that it was "extremely rare" for an otherwise healthy person to accidentally drown in a bathtub, unless alcohol or drugs were factors, which, he said, were not in Savio's case.

He also described how Savio's body was partly mummified and skeletonized by the time he examined it in 2007. He said decomposition was accelerated because water had gotten into her coffin. But, he said, autopsy work could still be performed.

Blum said he cut into parts of Savio's body, including on her hip, to discover that some bruises went almost to the bone, suggesting a major force caused the injuries. Blum also looked at photographs from the original autopsy and crime scene to make his determination.

Meczyk pressed Blum about how he could be sure Savio's bruises were freshly made before she died. Bruises that were days old are less likely to have been a factor in her death.